LESSON 5 Flashcards
A multicellular organism needs to coordinate _____ across different tissues & organs
cell division
critical for normal growth,
development & maintenance
cell division
not all cells can have the same ____
cell cycle
____ of cell division varies by cell type
Frequency
embryo
- cell cycle < ______
20 minute
skin cells
- divide frequently throughout life ________cycle
12-24 hours
liver cells
- retain ability to divide, but keep it in reserve divide once every _________
year or two
cell cycle 20mins
embryo
12-24 hrs cycle
skin cell
divides only once or twice a year
liver cells
do not divide at all after maturity permanently in G0
Two irreversible points in cell cycle
- replication of genetic material
- separation of sister chromatids
- process is assessed & possibly halted
Checkpoints
cell cycle controlled by STOP & GO chemical signals at critical points
checkpoints
signals indicate if key cellular
processes have been completed correctly
checkpoints
3 major checkpoint
G1/s, g2/m, spindle fiber scheckpoint
can DNA synthesis begin?
`g1/s checkpoint
has DNA synthesis been completed correctly?
g2/m checkpoint
commitment to mitosis
g2/m checkpoint
are all chromosomes attached to spindle?
spindle checkpoint
can sister chromatids separate correctly?
spindle checkpoint
primary decision point
- “restriction point”
g1/s checkpoint
if cell receives “GO” signal, it _____
divides
internal signals: ______, ______
cell growth (size), cell nutrition
external signals: “____-______”
growth factors
if cell does not receives signal, it exits cycle & switches to _______________
G0 phase
non-dividing, working state
g0 phase
non-dividing, differentiated state
g0 phase
in G0, but can be “called back” to cell cycle by external cues
liver cells
highly specialized
- arrested in G0 & can never divide
nervous & muscle cells